JPH1196563A - Optical information recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely detect a track position without being affected with a change in an input signal by providing a circuit extracting a low frequency component showing the envelope of the signal obtained on the track position and reflecting it to a reference value in the circuit generating a track signal of on/off. SOLUTION: The signal A obtained when an optical pickup traverses a track on a disk is inputted to a track position detection circuit, and the signal B showing the envelope of the signal A is extracted by a low-pass filter LPF 1, and the envelope of the signal B is detected by a peak hold circuit 2 of a reference value generation circuit 2, and fluctuation in a DC level is obtained approximately, and an offset value of a reference offset power source 24 is added to it to be made the reference value R. The reference value R is compared with the output signal B of the LPF 1 by a comparator 3, and a comparison output D making 'off' when the signal B is larger than the reference value R, and making 'on' when smaller is outputted. Thus, whether the pickup exists respectively on the track or between tracks is detected by the on/off signal of the signal D.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical recording / reproducing apparatus, and more particularly to detection of on-track / off-track of an optical pickup in an optical recording / reproducing apparatus.

[0002]

2. Description of the Related Art A conventional optical recording / reproducing apparatus will be briefly described with reference to FIG. As shown in FIG. 1, the optical recording / reproducing apparatus rotates a disk 1 around a spindle 2 by a spindle motor 3, writes information on the disk 1 by an optical head (optical pickup 4), and writes information on the disk 1. The information recorded along the track is read by the optical pickup 4.

[0003] Tracks are formed in the circumferential direction (rotation direction) on the disk, and a plurality of tracks are arranged in the radial direction. This will be described later with reference to FIG.

The optical pickup 4 can move in the radial direction of the disk by the operation of the access circuit 6,
Thus, the optical pickup 4 can be sequentially moved in the radial direction at the time of accessing the target track or at the time of recording and reproduction.

Now, the operation at the time of reproduction will be described. An information signal optically detected by the optical pickup 4 is sent to a demodulation circuit 5, where it is demodulated, and an information signal such as audio and video is sent to a subsequent circuit. , After signal processing.

The control signal of the signal demodulated by the demodulation circuit is sent to the control circuit, and a signal for controlling the number of rotations of the motor is taken out. It is used to extract a signal for controlling the focusing so as to be focused, or to extract a tracking signal for controlling the light emitted from the optical pickup to be projected on a track.

FIG. 4 shows a waveform of a disk 1 and a signal reproduced from the disk. (A) of the figure is a view of the disk as viewed from above, and (B) of the figure is a-
It is sectional drawing cut | disconnected along a '. The size of the disc and the number of tracks are different from the actual ones due to space limitations, but it will be a reference for understanding the concept.

On the disk 1, a plurality of tracks extending in the circumferential direction are formed side by side in the radial direction, and when the optical pickup 4 moves in the radial direction, the amplitude on the tracks as shown in FIG. Is maximized, and a signal waveform whose amplitude is minimized between tracks appears.

The number of tracks crossed by the optical pickup can be counted by counting the pulses obtained by amplifying the signal waveform in (c) and shaping the waveform.

[0010]

In the above-mentioned track crossing signal waveform, the center line does not always maintain a constant value as shown in (c) of FIG. The center line fluctuates as shown. For example, (b)
As shown by a dotted line, if the disk 1 is warped, if the warp is at one location, undulations are repeated at a cycle of one rotation of the disk.

This phenomenon occurs not only when the disk is warped as described above, but also when the light beam emitted from the laser light source of the optical pickup 4 fluctuates. Furthermore, a similar phenomenon occurs due to a change in the sensitivity of the optical sensor of the optical pickup.

As described above, the signal waveform (c) is shaped into a pulse signal. At this time, if the signal is larger than the reference value, it is turned on, and if smaller, it is turned off. However, if the reproduction signal fluctuates as shown in the signal waveform (d) while the reference value remains constant, correct detection may not be performed.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the above-mentioned drawbacks of the track position detecting circuit and eliminate the influence of a periodic DC fluctuation component included in a detection signal.

[0014]

In order to solve the above-mentioned problems, the present invention provides an optical recording / reproducing apparatus having the following means. That is, the optical information recording / reproducing apparatus of the present invention obtains a track detection signal by moving an optical pickup in a direction crossing a plurality of tracks on an optical recording medium on which a plurality of tracks are arranged in parallel. A low-pass filter for extracting a track detection signal from signals detected by the optical pickup, and a DC level included in the track detection signal. A reference value including a hold circuit that extracts and holds a fluctuation component, an offset power supply that generates an offset value unique to each device, and an addition circuit that adds the offset value to the output of the hold circuit to generate a reference value A generation circuit; and a comparison circuit for comparing the output signal of the low-pass filter with the reference value. Then, an on-track / off-track signal is output to the output of the comparison circuit.

The cut-off frequency of the low-pass filter of the track position detection circuit is set to a value that allows the passage of the track detection signal.

The offset value of the offset power supply of the track position detecting circuit is made variable so that it can be set to a set value determined according to the state of the recording medium, drive system, optical pickup and the like.

[0017]

An embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a basic configuration of a track position detecting circuit of the present invention, and FIG. 2 shows operation signal waveforms of the detecting circuit of FIG.

The track position detecting circuit shown in FIG. 1 is a circuit provided in the optical recording / reproducing apparatus described with reference to FIG. 3, and an input signal A to the track position detecting circuit is such that the optical pickup operates in the radial direction of the disk. And the signal obtained when the vehicle crosses the track and is shown in FIG.

A low-pass filter LPF1 is provided to extract a track detection signal B (FIG. 2B) representing the average value of the amplitude of the signal A. That is, by setting the cut-off frequency of the low-pass filter (low-pass filter, LPF) 1 to an appropriate value, the signal B representing the envelope (envelope) of the signal A can be extracted.

The output signal B of the LPF 1 shown in FIG. 1 has a waveform shown in FIG. As is apparent from FIG. 6, the DC level of the signal B fluctuates due to a low-frequency noise component caused by the warpage of the disk or the offset of the optical sensor.

The fluctuation of the DC level can be approximately obtained by detecting the envelope of the signal B. Therefore, the reference value generation circuit 2 in the circuit of FIG. 1 detects the envelope of the signal B by using the peak hold circuit 23 in order to correct this variation.

Although the peak hold circuit 23 can be constituted by using a diode and a capacitor, the present invention does not particularly have a gist in this respect. is there.
The peak detection circuit 21 detects the peak of the signal B, and the hold circuit 22 holds the peak value. The value held by the hold circuit 22 is a value representing the variation of the DC value, and the reference value R is obtained by adding the offset value of the reference offset power supply 24 to this value.

Whether to perform peak hold, bottom hold, or both can be determined as appropriate. Therefore, although the present embodiment is described as a peak hold circuit, a similar function can be obtained as a bottom hold circuit.

The signal C obtained from the hold circuit 22
Is the peak value of the amplitude waveform of the signal B, as shown in FIG. 2C, and the peak value fluctuates due to the noise signal due to the above-mentioned disk warpage or the like.

In FIG. 1, an offset power supply 24 adds a proper offset value to the amplitude value held by the peak hold circuit 23 to generate a reference value R which is an intermediate value of the signal B. 3 to one input. The other input of the comparator 3 is the LPF
One output B is applied and compared with this reference value.

The state of this comparison is shown in FIG. Since the reference value R obtained by adding the offset value S to the hold value C has the same amplitude change as that of the signal B, the signal B is always compared with the reference value R near the center between the peak and the bottom. Can be compared.

Therefore, the output of the comparator 3 in the position signal detection circuit shown in FIG. 1 outputs a comparison output D that turns off if the amplitude of the signal B is larger than the reference value R and turns on if it is smaller than the reference value R. If the signal D is off, the optical pickup is on the track, and if the signal D is on, it indicates that the optical pickup is between the tracks.

In the above circuit operation, if the amplitude of the output signal B of the LPF 1 is too small to detect accurately, the amplitude of the signal B is amplified by giving a gain to the LPF 1 or inserting an amplifier in the subsequent stage. To a value sufficient for signal detection.

When the envelope of the signal A, that is, the signal B is extracted by the above method, it is only necessary to adjust the cutoff frequency of the LPF 1 so that the frequency of the signal B is passed. Therefore, the setting of the LPF 1 is easy, so that the setting of the LPF 1 is easy.

As described above, the cut-off frequency of the LPF 1 is set so as to block a high-frequency signal component caused by the information signal recorded on the disc and to pass only the envelope, but to read the information signal. When the speed changes, the frequency of the signal A changes. When the moving speed of the optical pickup in the cross-track direction changes, the frequency of the envelope signal B changes.
The cutoff frequency of LPF1 is made variable so that the cutoff frequency of LPF1 can be changed accordingly.

The characteristics of the optical sensor used in the optical pickup have some variation for each device, and the offset value differs for each device due to this variation. Therefore, this offset is measured in advance for each device and adjusted to an appropriate value.

The signal A may be lost and the signal B may not be obtained due to scratches or dirt on the disk. In such a case, when the signal B disappears, the center of the maximum value and the minimum value of the fluctuation of the peak value is stored in the hold circuit so that the signal B is quickly returned to the original state after the signal B is obtained again. To maintain the value of. To satisfy this requirement, the time constant of the hold circuit can be set.

Further, the period of signal loss caused by the warp or scratch of the disk varies depending on the reading speed of the recording signal. Therefore, the time constant of the hold circuit can be selected so as to select a time constant suitable for this. Make it variable. Further, the offset is made variable according to the change.

[0034]

When the optical pickup is moved in the cross-track direction, a signal obtained from the track position is compared with a reference value, and a signal generated at the track position is generated by an on-track or off-track signal according to the magnitude of the reference value. By providing a circuit for extracting a low-frequency component of the signal B indicating the envelope of A and reflecting the low-frequency component on the reference value, the circuit is not affected by changes in the input signal due to the warpage of the disk or periodic noise mixed into the optical pickup or the like. Detection becomes possible.

The voltage value to be held in the hold circuit depends only on the low-frequency component included in the track detection signal and is independent of other factors. Therefore, when performing double-speed reproduction or the speed at which the optical pickup crosses the track. When the time has changed, the operation of setting the time constant of the hold circuit to the optimum value can be easily performed. By giving the reference value an offset that does not affect the on-track and off-track signals, the initial value of the comparator output can be determined.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of a position detection circuit according to the present invention.

FIG. 2 is a waveform chart showing operation waveforms of respective parts of the circuit of FIG. 1;

FIG. 3 is a block diagram illustrating a system configuration of the optical recording / reproducing apparatus.

FIG. 4 is a schematic diagram showing a disk and a reproduction signal waveform.

[Explanation of symbols]

1 low-pass filter, 2 reference voltage generating circuit, 3
‥‥ Comparison circuit

Claims (3)

[Claims] 1. A track position detecting circuit for moving an optical pickup in a direction crossing a plurality of tracks in an optical recording medium having a plurality of tracks arranged in parallel to obtain a track detection signal. In the optical information recording / reproducing apparatus, the track position detection circuit includes: a low-pass filter for extracting a track detection signal from signals detected by the optical pickup; and a DC level fluctuation component included in the track detection signal. A reference value generation circuit including a hold circuit that extracts and holds the data, an offset power supply that generates an offset value unique to each device, and an addition circuit that adds the offset value to the output of the hold circuit to generate a reference value And a comparison circuit for comparing the output signal of the low-pass filter with the reference value. Optical information recording and reproducing apparatus without to output a track / off-track signal. 2. The optical information recording / reproducing apparatus according to claim 1, wherein a cutoff frequency of the low-pass filter is set to a value that allows the track detection signal to pass. 3. The optical information recording / reproducing apparatus according to claim 1, wherein said offset value is variable so as to be set to a set value determined according to a state of a recording medium, a drive system, an optical pickup, and the like. apparatus.